Part art, part science, good, distinctive interior design depends on a few simple principles about how to use space and how people live in a home, plus a knowledge of what’s on the market, whether the demand of the day calls for antique, midcentury modern, or contemporary furnishings. There are no firm rules, but it’s a good idea to get acquainted with what professionals say works and what doesn’t, consider your family’s needs, and keep up with the latest innovations.